In the process of acquiring seismic data within a survey area, shot points and listening points are laid out typically in a grid like fashion with listening points in lines called receiver lines and shot points in lines called source lines. Source lines and receiver lines are also typically perpendicular or at some nominal angle to one another. It is also common that no shot point is directly on a listening point. The design of the survey is a balance between resolution and cost where more shot points and listening points provide higher resolution at higher cost although terrain, topography and structures at the surface must also be accommodated.
It should be understood that a survey is rarely conducted where an autonomous recorder is positioned at every listening point during the entire survey. Typically, the survey covers an area so large that most listening points are out of the range of seismic energy being broadcast from any shot point in the survey. Thus, as one would expect, a survey begins with laying out the autonomous recorders within range of the first shot points and then continually moving autonomous recorders that fall out of the range to the front of the survey as the seismic source trucks progress from shot point to shot point shaking each one. However, with conventional cable geophones, the conventional pattern of progression has been to lay out long cables of geophones to extend the full length of the receiver lines and also to cover the width of the range of useful, recordable seismic energy. Thus, if the range for a useful, recordable signal is 12 receiver lines wide, for example, then normally 13 cables worth of equipment are brought to the field and laid out for the survey. In the conventional pattern, the source trucks move from shot point to shot point along and within a “valley” between two adjacent receiver lines so that the entire signal at each shot point is captured by geophones in the field. This is normally called “template centered shooting”. When the source truck gets to the end of a valley, it moves over to the next adjacent valley and progresses back toward the first end of the survey area. If several seismic trucks are used concurrently, then each truck would typically stay within a single valley and progress along in adjacent valleys but generally side-by-side until all the shot points in each valley were complete and then all move to the next set of adjacent valleys. When the seismic source trucks reach the ends of the first valley or valleys to move to a second set of valleys, if one or more lines of geophones become out of range, they are collected up and moved to the next open receiver lines. By the time the seismic source trucks reach the ends of the second set of valleys to move over to the third set of valleys, the receiver lines are to be ready and in place for steady progression and efficiency.
Now, with the advent and wider use of autonomous, continuously recording seismic data recorders, having geophones strung along with cables are less common and not required. But the procedure for laying out the autonomous recorders and shaking shot points has not changed.